1. Field of the Invention
The present invention concerns a laser beam guidance device for a civil engineering/earthmoving plant controlled by means of actuators and required to move along a predetermined path having a three-dimensional surface, the device being of the kind using a laser emitter and two laser receivers.
2. Description of the Prior Art
A preferred but by no means exclusive application of the present invention is to guiding machines for surfacing roads or paths in three dimensions. These are wide machines (approximately 10 m wide) which at present are guided by means of wires stretched along either side of the road or path to be surfaced. These surfacing machines are well known and include, for example, the GP-2500 machine manufactured and marketed by the company Gomaco Corporation of Ida Grove, Iowa.
Using a guidance device of this kind is in practice somewhat complicated and time-consuming given the large number of operations required to lay the wires. Also, if the road or path is curved, the curve is approximated by a series of straight line segments along which the guide wires must be stretched, which increases the number of operations required to install and adjust the guidance device, especially when the machine reaches junctions between the segments.
One objective of the present invention is, therefore, to simplify the guidance device without requiring significant modification to the machine.
British Patent No. 2,228,507 discloses a surfacing machine embodying a tool adapted to be positioned heightwise relative to the machine and to the surface worked on, two laser receivers disposed on actuators mounted above the tool so that they move the laser receivers in a vertical direction, a device for measuring the distance travelled and logic responsive to signals from the receivers and the distance measuring device adapted to control the actuators. The laser receivers cooperate with a laser emitter mounted a predetermined height above the surface to be worked on and adapted to scan a laser beam in a reference plane.
The logic stores the required surface profile in memory. In response to logic signals transmitted by the laser receivers and the distance measuring device, the logic controls the actuators to maintain the receivers in the reference plane and positions the tool to shape the surface according to the stored profile.
Note that this machine can only position the tool relative to the reference plane along an axis perpendicular to the latter. It is, therefore, unable to guide the machine along a path or road with a three-dimensional surface. In particular, it is unable to guide the machine around a curve.
What is more, because the laser beam scans a large surface area and impinges on the receivers at two points only therein, much laser light energy is dissipated into the atmosphere. As the beam is not collimated at the receiver a high energy input is required to obtain a long range.
The present invention is directed to a guidance device implementing some of the teachings of British Patent No. 2,228,507 but adapted to guide a machine for shaping a three-dimensional surface, in particular for surfacing roads or paths, where the latter are curved, while being more efficient than the prior art machine described above.